Patches are known that comprise a backing sheet coated on one face in a layer forming a reservoir known as a "matrix", containing one or more active substances that are to be diffused into the skin and/or that are to act thereon.
The matrix can be made of a material having adhesive properties, whether intrinsic or otherwise, in which case the patch has an adhesive coating on its surface.
In which case, it is necessary to ensure that the coating does not impede the action of the active substance(s) contained in the matrix.
The invention relates more particularly to a patch in which the matrix is made of a material presenting intrinsic adhesive properties.
Selecting this material raises difficulties, and in particular:
it must be capable of containing the active substance(s) for acting on the skin; PA1 its adhesion to the skin must not be too strong, particularly if it is to be applied in repeated manner, since otherwise the region of the body on which the patch is applied will be come irritated, and removing the patch will become painful; PA1 its adhesion must not be too weak either, since otherwise it will not be able to adhere to the skin if it is moist or if it becomes moist, e.g. because of sweating; PA1 it must be sufficiently flexible to allow the patch to fit over the shape of the region of the body on which it is applied; PA1 it must remain on the backing sheet when the patch is removed; and PA1 finally, it must make it possible to extract the impurities that are to be found on the surface of the skin, in particular sebum or sweat.
In spite of these difficulties, several materials have been proposed for making the matrix, however they are not necessarily suitable for all of the active substances that it might be desirable to incorporate therein.
French patent 2 738 744 or European patent 0 309 309 teach in particular the use of hydrophobic or hyposoluble materials for constituting the matrix.
The hydrosoluble material described in European patent 0 309 309 is relatively impractical in use since it does not present the required adhesive properties prior to application to the skin and it requires the skin to be previously moistened.
European patent application EP-A-0 412 869 describes a composite film having a silicone polymer matrix adjacent to an occlusive matrix. On its side remote from the occlusive layer, the matrix has a reinforcement--constituting screen and a removable protective membrane. The screen reduces the adhesive area of the protective membrane on the matrix.
In such a composite film, the screen locally prevents the matrix from coming into contact with the skin. When the film is withdrawn, the screen runs the risk of leaving a mark on the skin with the mark being all the more pronounced with increasing adhesion of the material constituting the matrix. For a silicone polymer matrix, whose adhesive power (TAC) is relatively low (about 100 g/cm.sup.2), this drawback is nevertheless not too troublesome. Finally, the screen prevents a mechanical cleansing action being exerted on the entire area of the skin that is covered by the film.